Reliably separating fluids, such as water, oil, and gas, is critical in petroleum, medical, biological, and analytical chemistry applications, just to name a few. Separating fluids enables specific measurements to be performed on the particular fluid. For example, emulsion separation is necessary for the proper disposal of waste streams, purification in petroleum production, and the recovery of products from micro-reactors. Of particular interest in this application is the separation of emulsions, liquid/liquid extraction, and particle/molecule extraction and/or separation.
Conventional methods of emulsion separation involve, for example, addition of demulsifying agents, gravity separation, centrifugation, hydrocyclone separation, and air flotation. Aside from having high operating costs, these methods suffer from poor performance, often resulting in incomplete separation. Typically traces of contaminants remain in the fluid of interest. Additionally, conventional separation techniques often take a long time, depending on the particular composition of the fluid. For example, a fine emulsion may take months to separate by gravity.
Additionally, conventional emulsion separation methods usually involve large volumes, and tend not to be suitable for smaller scale separations. Current methods for small scale emulsion separation require the application of an external electrical signal as disclosed in HUNG ET AL., A Microfluidic Platform for Manipulation and Separation of Oil-in-Water Emulsion Droplets using Optically Induced Dielectrophoresis, JOURNAL OF MICROMECHANICS AND MICROENGINEERING. 20 (2010) 1; and FIDALGO ET AL., From Microdroplets to Microfluidics: 3 Selective Emulsion Separation in Microfluidic Devices, CHEM. INT. ED. 47, 2042-2045 (2008). Other methods employ the use of a pore comb structure as disclosed in ANGELSCU ET AL., Microfluidic Capillary Separation and Real-Time Spectroscopic Analysis of Specific Components from Multiphase Mixtures, ANALYTICAL CHEMISTRY, Vol. 82, No. 6 (2010).
Conventional methods of liquid-liquid extraction include bubble columns, requiring a significant density difference between the two liquid phases. Other methods of liquid-liquid extraction include microfluidic droplet-based extraction or electrochemically modulated extraction as disclosed in BERDUQUE ET AL., Microfluidic Chip for Electrochemically-Modulated Liquid/Liquid Extraction of Ions, ELECTROCCHEMISTRY COMMUNICATIONS, 10 (1), 20-24 (2008). Droplet-based extraction requires a separation method after extraction, and electrochemically modulated extraction requires the application of an external field.
Conventional methods of particle separation include filtration and centrifugation. However, filtration is often undesirable because of the potential of crushing particles and the inability to process large volumes of solution as particles collect. Centrifugation tends to be undesirable when there is a density difference within the particle, which happens, for example, when the particle is used to encapsulate another material. The harsh forces involved in centrifugation could cause the particle having different densities to rupture. Both filtration and centrifugation subject particles to undesirable shear stresses and/or suffer low particle yield.
More recently developed methods of particle separation use field-flow fractionation, dielectrophoresis and shear induced separation. Both field-flow fractionation and dielectrophoresis require the application of an external field, making those methods less desirable for transition to the industrial scale. Shear induced separation employs the use of a membrane making this method less desirable due to the potential for solids related damage or membrane fouling.
Both U.S. Pat. No. 7,695,629 to Salamitou et al and U.S. Pat. No. 7,575,681 to Angelescu et al. disclose the use of a separation and filtration device employing a porous membrane employing oleophobic pores for tangential flows there through for filtration. These devices employ complicated filtration mechanisms without channels and are on the micro as opposed to milliliter scale. U.S. Pat. No. 7,390,463 to He et al. discloses the use of an array of vertically oriented fluidic modules or micro-columns having fluidic microchannels, which serve as a conduit for introducing reagent or media solutions to the biological assay device for analysis. Again, this device is on the micro scale and is complex.
U.S. Published Patent Application No. 2011/0032513 to Joanicot et al. discloses both microfluidic and millifluidic flow channels. However, this device is exceeding complex, with intricate channels engraved on a plate, including an intricate array of feed channels, connector channels and even storage channels in the device.
Accordingly, there is a need for a microfluidic separator mechanism capable of emulsion separation, liquid/liquid extraction, and particle separation and/or extraction that does not require membranes, electrical fields, or additives, and may be manufactured simply and economically. The present invention fulfills this need among others.